Chemical plating of metal-boron alloys



United States Patent Pennsylvania I No Drawing. Filed Aug. 5, 1958, Ser. No. 753,192

8 Claims. (Cl. 117-130) This invention relates to a method of chemical plating and more particularly to a method of plating metal objects with metal-boron alloys.

Nickel-boron and cobalt-boron alloys are known for their superior flowing properties, wear resistance, and hardness. Metal boron alloys, or metal borides, are particularly useful as coatings for steel and other metals that do not possess these desirable properties. The metalboron alloys are also useful as catalysts for a number of chemical reactions, e.g., hydrogenation reactions. Coatings of metal-boron alloys on other metallic base materials are particularly desirable as catalysts since a maximum amount of catalytic surface is provided by a minimum amount of the metal-boron alloy.

This invention is based on my discovery that an aqueous solution of an amine borane, X-BI-l Where X is an amine, and a soluble nickel or cobalt salt is a stable chemical plating solution. When a material with a catalytically active surface is contacted with this plating solution, a reaction occurs at the surface forming an adherent continuous plate of metal-boron alloy on the surface. The alloy plate itself is catalytically active so that the surface reaction can be continued to form a plate of any desired thickness. I have found that any clean metal surface, free of oxide film, is catalytically active. Glass, waxes, e.g. paraifinic waxes, natural fibers, and synthetic organic polymers, e.g. polyethylene and nylon, exhibit essentially no catalytic activity.

The solution or plating bath of this invention comprises an aqueous solution containing from about: (1) 0.02 to 6 parts by weight metal ion of the metal boron alloy to be plated, and (2) 0.1 to 3 parts by weight of boraneradical, EH

The metal ion, i.e. cobalt, or nickel ion, is provided by use of any soluble metal salt such as nickel sulfate, nickel chloride, nickel acetate, cobaltoussulfate, cobaltous chloride or other suitable soluble salts.

The borane radical is provided by the use of any secondary or tertiary amine borane, e.g. trimethylamine borane, dimethylamine borane, tripropylamine borane, pyridine borane and lutidine borane. Primary amine boranes are not satisfactory for use in the plating baths because they are rapidly decomposed by hydrolysis reactions.

The pH of the plating baths should be maintained below about 6.5; at higher pH values the plating reaction is extremely slow and some metal ion precipitates as the hydroxide. It is preferred to maintain the pH above about 2 because at lower pH values the solution is only metastable and tends to react spontaneously forming a large amount of particulate precipitate so that only a small proportion of the metal-boron alloy is plated. The initial pH of the aqueous plating solutions containing the metal salt and the amine borane are within the preferred range. As the plating reaction proceeds the pH of the solution increases because of the release of amine from the reacted amine borane. If the pH increases to too high a value, the solution can be acidified with any non-oxidizing acid, e.g. HCl. It is particularly convenient to buffer the plating solution with a weak, non-oxidizing acid, e.g. acetic acid or boric acid.

The plating baths of this invention have varying degrees of activity; the more active baths plate at a higher rate. The activity of the bath increases with increasing metal 2,990,296 Patented June 27, 1951 p ce 2 ion concentration and increasing borane radical concentration. The activity of the bath also increases with a decrease in pH. The plating bath may be used at any temperature between about room temperature and the boiling point of the solution with the activity of the bath increasing with increasing temperature.

The object to be plated is immersed in the plating bath and the plating commences. The object may conveniently be suspended by a string or rope made of-natural or synthetic fiber, or it may be suspended in a cloth or supported by a wood, glass, or synthetic polymer rack. If a metal piece is used to support the object to be plated, some of the bath will be consumed in plating the support. After the object has been plated, it is removed from the bath and washed with water to remove the bath solution and permitted to dry.

Metal objects to be plated must have clean surfaces free of oxide film. The objects are cleaned by any of the conventional cleaning procedures. The clean metal surface'catalyzes the chemical reduction reaction which results in a metal-boron alloy plate on the clean surface.

'Objects of steel, iron, nickel, cobalt, titanium, copper and copper base alloys, aluminum and aluminum base alloys, palladium, and other metals may be plated according to this invention.

It is preferred to contain the plating solution in a vessel that exposes only non-active surfaces to the bath. Glass vessels are most convenient, and synthetic polymer vessels, such as polyethylene vessels, and vessels lined with nonactive material may be ued, e.g., paraffin Wax lined, polyethylene lined, or polyvinylidine chloride lined vessels. The plating process is then selective; the plating occurs on the metal object immersed in the solution and does not occur on the vessel walls.

When plating has proceeded for several hours, a small amount of metal-boron alloy particulate precipitate is formed and collects at the bottom of the vessel. This precipitate is itself catalytically active so that if it is not removed some of the plating solution will be consumed by reaction induced by the precipitate. The precipitate may be removed by filtration.

The chemical plating consumes borane radical and metal ion; any desired concentration or concentration range may be maintained by adding additional amine borane or metal salts to the plating solution.

The following examples are illustrative of the plating solutions of this invention. The compositions of the solutions are expressed in weight percent of anhydrous reactants. The actual metal salts used were hydrates.

individual metal strips in aliquots of the plating solution for two hours at about 25 C Example II A plating solution was prepared which contained 0.95 wt. percent (CH NH-BH 5.14 wt. percent NiCl and 93.91 wt. percent water. The pH of the solution was 5.4. A carbon steel test panel was immersed in the solution maintained at 18 C. for 2 /3 hours. A nickel-boron alloy immediately started to plate on the steel panel. During the course of the plating reaction the pH increased to 6.13

and the rate of plating"decreased. The average rate of plate-deposition was-0.019 inches per'hour.

Exahiple [II 1:56 ate of fiofmatiori at mm allo plate is incr ased if t li solution ismiiifei'ed to reduce-the? increasedn pH (hiring thecouiseof' the reaction. For example. a buffered solution:contairiing' 3.7 'wt. percent (CH NH-BH ,9.3 wt. percenmsic1 wt; percent'H BO and 284.5 wt. percent water had-'apHof tQS. A nickel-boronalloy "was pl'ated'z on a" carbonsteel panel immersed in the solutionfo r 6%h ours at" 18 C. The average plating rate was 0.091 X1 0- inches "per'hour.

Eicizr'ri' 'pl lV Anadherent continuous nickel-boron plate was formed at an average rate of 0.014X10 inches per hour on a carbonsteel -panel by immersing it in a plating solution at-24" C. for 127 minutes. The plating solution contained 1.1 wt. percent (CH N-BH 5.1 wt. percent NiCl and '93.8% water. a

. Example V "Afca'rbon"s'fe e1'testpanelwas immersed in a plating solution containing 2.2'wt.percent (CH NH-BH 5.1 f'wt.percent CcCl and 92.7 wt. percent water. The avera'geplating rate was 0. O3 10* inches per hour for a two fh mmersion at'roomtemperature. During the plating reaction a small amount of particulate boron alloy precipitate was formed.

. Example VI bufiered' platingsolution containing 3.7 wt. percent 1((3 I-I3') NH-BH 10.1 wt. percent CoCl 2.5 wt. percent I- IBQ and 83.7wt. percent water hada pH of 4.02. A 'carbon steel panelwas immersed inthe solution at room ternperature for 297 minutes. A bright plate of cobaltboron'alloy'was plated on'the panel at an average rate of 0.25X1Q' inches per hour. The jniclgel-boron coatings formed by theprocess of j thisinvention'generally appear dark to semi-bright and the cobaltboron coatings generally appear semi-bright to bright. f The plated alloys contain from about 4 to 10 "pe ssa ihom .7 -Accordingto'theprovisions of the patent statutes, I have explained the principleand mode of practicing my 'iin entiOn'Qand haVe described what I'nowconsider to be its: best embodiments. However, I desire'to have it midersto'od' that within the scope of the appended claims,

the invention may be practiced otherwise than as specifically described.

I claim:

1. An aqueous chemical plating solution containing as essential components (1) a compound selected from the group consisting of secondaryand tertiary amine boranes and, (2) acompound selected'from the groupconsisting 'of soluble saltsof nickel and cobalt, the proportions of 'each' component being such that'the concentration' of borane radical isbetween'about 0.1 to 3 wt. percent, and the concentration of metal ion is between about 0.02 and 6 wt. percent.

2. A method of plating metal-boron alloys on metal "objects which comprises the step ofconta cting the object to be plated with an aqueous plating solution containing as essential components (1) a compound selected from the group consisting of secondary and tertiary amine boranes and. (2) a compound selected from the group consisting of soluble salts of nickel and cobalt, the proportions of each component being such that the concentration of borane radical is between about 0.1 to 3 wt. percent and the concentration'of metal ion is between about 0.02 and 6 wt. percent.

3. A method according to claim 2 in which the amine borane is dimethylamine borane.

4. A method according to claim 2 in which the pH of the plating solutionis maintained between about 2 and 6.5.

References Cited in the file of this patent V UNITED STATES PATENTS Schlesinger et al. Feb. 15, 1949 Warf Dec. 6, 1955 OTHER REFERENCES 'Hurdi Chemistry of the Hydrides, 1952 John Wiley 'andSons, pg. 84.

Notice of Adverse Decision in Interference In Interference No. 93,4:69 involving Patent No. 2,990,296, R. M. Hoke, Chemical plating of metal-boron alloys, final judgment adverse to the patentee was rendered Nov. 24:, 1964:, as to claims 1, 2, 3, 4c, 5, 7 and 8.

[Ofiioial Gazette J ammry 1.9, 1965.] 

2. A METHOD OF PLASING METAL-BORON ALLY ON METAL OBJECTS WHICH COMPRISES THE STEP OF CONTACTING THE OBJECT TO BE PLATED WITH AN AQUEOUS PLATING SOLUTION CONTAINING AS ESSENTIAL COMPONENTS (1) A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SECONDARY AND TERTIARY AMINE BORANES AND, (2) A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SOLUBLE SALTS OF NICKEL AND COBALT, THE PROPORTIONS OF EACH COMPONENT BEING SUCH THAT THE CONCENTRATION OF BORANE RADICAL IS BETWEEN ABOUT 0.1 TO 3 WT. PERCENT AND THE CONCENTRATION OF METAL ION IS BETWEEN ABOUT 0.02 AND 6 WT. PERCENT. 